[llvm] r269008 - [ValueTracking] Use guards to prove non-nullness of a value

[Sanjoy Das via llvm-commits]

Author: sanjoy
Date: Mon May  9 21:35:44 2016
New Revision: 269008

URL: http://llvm.org/viewvc/llvm-project?rev=269008&view=rev
Log:
[ValueTracking] Use guards to prove non-nullness of a value

Reviewers: apilipenko, majnemer, reames

Subscribers: mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D20044

Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp
    llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=269008&r1=269007&r2=269008&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Mon May  9 21:35:44 2016
@@ -3212,17 +3212,19 @@ static bool isKnownNonNullFromDominating
       continue;
 
     for (auto *CmpU : U->users()) {
-      const BranchInst *BI = dyn_cast<BranchInst>(CmpU);
-      if (!BI)
-        continue;
+      if (const BranchInst *BI = dyn_cast<BranchInst>(CmpU)) {
+        assert(BI->isConditional() && "uses a comparison!");
 
-      assert(BI->isConditional() && "uses a comparison!");
-
-      BasicBlock *NonNullSuccessor =
-          BI->getSuccessor(Pred == ICmpInst::ICMP_EQ ? 1 : 0);
-      BasicBlockEdge Edge(BI->getParent(), NonNullSuccessor);
-      if (Edge.isSingleEdge() && DT->dominates(Edge, CtxI->getParent()))
+        BasicBlock *NonNullSuccessor =
+            BI->getSuccessor(Pred == ICmpInst::ICMP_EQ ? 1 : 0);
+        BasicBlockEdge Edge(BI->getParent(), NonNullSuccessor);
+        if (Edge.isSingleEdge() && DT->dominates(Edge, CtxI->getParent()))
+          return true;
+      } else if (Pred == ICmpInst::ICMP_NE &&
+                 match(CmpU, m_Intrinsic<Intrinsic::experimental_guard>()) &&
+                 DT->dominates(cast<Instruction>(CmpU), CtxI)) {
         return true;
+      }
     }
   }
 

Modified: llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll?rev=269008&r1=269007&r2=269008&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll (original)
+++ llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll Mon May  9 21:35:44 2016
@@ -469,5 +469,90 @@ for.end:
   ret void
 }
 
+declare void @llvm.experimental.guard(i1, ...)
+
+define void @test12(i32* noalias %a, i32* %b, i32* dereferenceable_or_null(4) %c, i32 %n) #0 {
+; Prove non-null ness of %c via a guard, not a branch.
+
+; CHECK-LABEL: @test12(
+entry:
+  %not_null = icmp ne i32* %c, null
+  call void(i1, ...) @llvm.experimental.guard(i1 %not_null) [ "deopt"() ]
+  %cmp11 = icmp sgt i32 %n, 0
+  br i1 %cmp11, label %for.body, label %for.end
+
+; CHECK: for.body.preheader:
+; CHECK-NEXT:  [[VAL:%[^ ]]] = load i32, i32* %c, align 4
+; CHECK-NEXT:  br label %for.body
+
+
+for.body:                                         ; preds = %entry, %for.inc
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4
+  %cmp1 = icmp sgt i32 %0, 0
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:                                          ; preds = %for.body
+  %1 = load i32, i32* %c, align 4
+  %arrayidx3 = getelementptr inbounds i32, i32* %b, i64 %indvars.iv
+  %2 = load i32, i32* %arrayidx3, align 4
+  %mul = mul nsw i32 %2, %1
+  store i32 %mul, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body, %if.then
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.inc, %entry, %entry
+  ret void
+}
+
+define void @test13(i32* noalias %a, i32* %b, i32* dereferenceable_or_null(4) %c, i32 %n) #0 {
+; Like @test12, but has a post-dominating guard, which cannot be used
+; to prove %c is nonnull at the point of the load.
+
+; CHECK-LABEL: @test13(
+entry:
+  %not_null = icmp ne i32* %c, null
+  %cmp11 = icmp sgt i32 %n, 0
+  br i1 %cmp11, label %for.body, label %for.end
+
+; CHECK: for.body.preheader:
+; CHECK-NOT:  load i32, i32* %c
+; CHECK:  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.inc
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4
+  %cmp1 = icmp sgt i32 %0, 0
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:                                          ; preds = %for.body
+; CHECK: if.then:
+; CHECK:  load i32, i32* %c
+; CHECK:  br label %for.inc
+  %1 = load i32, i32* %c, align 4
+  %arrayidx3 = getelementptr inbounds i32, i32* %b, i64 %indvars.iv
+  %2 = load i32, i32* %arrayidx3, align 4
+  %mul = mul nsw i32 %2, %1
+  store i32 %mul, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body, %if.then
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.inc, %entry, %entry
+  call void(i1, ...) @llvm.experimental.guard(i1 %not_null) [ "deopt"() ]
+  ret void
+}
+
 attributes #0 = { nounwind uwtable }
 !0 = !{i64 4}